1. Field of the Invention
The present invention relates to braking system wear indicators and particularly to a brake lining wear indicator for an “S” cam type truck brake wherein an indicator is mounted on the slack adjuster lever arm and S cam shaft, which gives visual reference to the condition of the brake lining.
2. Description of the Prior Art
Most air braking systems for trucks have drum-type brakes with two arcuate shoe arms pivotally carried at first adjacent ends inside a brake drum for expansion against the inner surface of the drum to cause frictional braking action. The shoe arms are expanded by an “S” cam that is rotated between second adjacent ends of the opposed arms to cause both shoe arms to move radially outwardly in substantially similar fashion. A diaphragm type canister is normally provided that applies motive force to an actuator arm or lever which can include a slack adjuster mechanism that in turn rotates the “S” cam shaft for braking. A valve operated by the vehicle brake pedal releases compressed air to the canister to move the diaphragm. This system gives little, if any indication of brake wear condition to an operator.
Prior art devices do not provide indicators for brake wear which provide accurate visual wear indicators that can easily be viewed in a normal truck walk around inspection.
U.S. Pat. No. 5,320,198 issued Jun. 14, 1994 to Hoyt, is for an indicator for indicating the setting and linear stroke movement of a brake rod of a brake assembly. The gage includes reference indicators that are located on both the brake rod's clevis and on the arm of the brake's slack adjustment member, thereby indicating the brake rod travel and the need for brake adjustment.
U.S. Pat. No. 5,535,854, issued Jul. 16, 1996 to Prince, provides a one piece brake lining wear indicator gauge which is a reversible circular dial. Calibration marks are included on both sides of the circular dial along with several accentuating notches on the outside circumference of the dial. When the dial is coupled to the splined end of a rotatable brake shoe camshaft equipped with manual or automatic slack adjusting levers, the dial acts as an indicator of the amount of brake lining wear that occurs inside the brake drum compartment.
U.S. Pat. No. 6,390,244, issued May 21, 2002 to Sitter, shows a brake wear indicator that provides visual and tactile indication of unacceptable brake wear. The brake wear indicator has a hub drive attached to a cam shaft, a brake wear disk attached to the hub drive and a body attached to a slack adjuster lever. The brake wear disk has a wear detector lug. The body has two the travel limit lugs which extend towards the centerline of the brake wear disk and are on the end of flexible fingers. When the brake linings are approaching unacceptable wear, the wear detector lug contacts one of the travel limit lugs and pushes the travel limit lug and the end of the corresponding finger away from the adjacent outer surface of the body. The rising of the end of the finger above the adjacent surface provides visual and tactile indication of unacceptable brake wear.
U.S. Pat. No. 3,356,188, issued Dec. 5, 1967 to Goldman, claims a brake lining wear indicator that comprises a dial and an indicating plate. The dial attaches to the S-Cam shaft and the indicating plate attaches to the slack adjuster lever. When new brake linings are installed and the brakes are properly adjusted a central lip on the dial corresponds with a tang on the indicating plate. As the brakes wear and the slack adjuster is adjusted the dial rotates with respect to the indicating plate. When the brake linings are completely worn and the brakes are properly adjusted, the tang corresponds with one of two lips on the dial.
U.S. Pat. No. 5,358,076, issued Oct. 25, 1994 to Lucas, describes an indicator unit for a vehicle air brake system which includes a brake rod mounted for movement between a non-braking first position and a predetermined safe maximum braking second position. A pivotally mounted slack adjuster is connected to the brake rod and is responsive to the movement of the rod. An indicator unit is provided which has a first section removably mounted on the connection between the rod and adjuster, a second section retained in a predetermined alignment with the rod, and a third section angularly disposed relative to the second section. The unit third section is provided with angularly disposed, exposed, first and second reference marks. When the rod is in the first position, the first reference mark is aligned with a predetermined first segment of the adjuster. When the rod is in the second position, the second reference mark is aligned with the predetermined segment of the adjuster. The alignment of the second reference mark with the adjuster segment is indicative that the rod has traversed 80%, or the limit, of its safe braking stroke and thus indicates adjustment of the brake system is warranted.
U.S. Pat. No. 2,379,796, issued Jul. 3, 1945 to Freeman, discloses a brake operating mechanism having a cam operating shaft with an operating arm mounted thereon, said shaft further having a pointer and a scale thereon for indicating the adjusted position of the cam.
U.S. Pat. No. 2,522,903, issued Sep. 19, 1950 to Shively, indicates a brake operating and adjusting mechanism having a cam shaft with an anchor arm and a cap mounted thereon, both of which have indicating marks that cooperate to show how much take up has been made from the initial position on the cam shaft.
U.S. Pat. No. 6,059,074, issued May 9, 2000 to Crewson, is for a gauge for visually indicating travel of a brake operating rod having one end pivotally connected to a slack adjuster including a plate bearing indicia, which is mounted for movement with the one end of the brake operating rod, and a pointer pivotally supported on the slack adjuster and arranged to point to the indicia, wherein the pointer is coupled to the plate to cause the pointer to pivot relative to the adjuster and swing relative to the indicia, during travel of the brake operating rod.
U.S. Pat. No. 5,762,165, issued Jun. 9,1998 to Crewson, shows indicia applied to opposite side surfaces of a housing of a slack adjuster for vehicle brakes and a pointer is fixed for movement with a connector serving to pivotally connect the housing to a brake operating rod; the pointer cooperating with the indicia to provide visual indication of when the brake operating rod is in a retracted brake release position and when movement of such operating rod away from the brake release position exceeds a desired limit of brake operating movement.
U.S. Pat. No. 5,441,128, issued Aug. 15, 1995 to Hoyt, provides a bracket body which is easily affixed to the brake rod and clevis member of conventional brake adjustment apparatus of air-actuated braking mechanism, and provides indirect measurement of brake rod travel and adjustment, by the body showing the amount of angular rotation of the brake's adjuster member, even though brake rod travel is a generally linear stroke movement. The bracket body has a central body portion from which extends two extension members, a first one of the extension members being provided with attachment for the clevis and brake rod assembly, and the central body portion with attachment to the clevis pin. The second extension member provides the visual reference by relevance to the adjuster member.
What is needed is a visual indicator device showing brake lining condition which is highly visible to a driver in a simple walk around inspection of the truck without climbing under the truck.